#!/bin/python3

import sys
from collections import Counter

n = int(input().strip())
a = [int(a_temp) for a_temp in input().strip().split(' ')]

numcounts = dict(Counter(a))
maxcounts = 0
for i in numcounts.keys():
    count1 = numcounts.get(i-1, 0)
    count2 = numcounts.get(i, 0)
    count3 = numcounts.get(i+1, 0)
    
    intercount1 = count1+count2
    intercount2 = count2+count3
    
    intercount = max(intercount1, intercount2)
    
    if intercount > maxcounts:
        maxcounts = intercount
        
print(maxcounts)